Robotic surgical system and method for automated therapy delivery

ABSTRACT

A method of navigating a medical device through a body of a patient includes providing a topography of at least a portion of the body, accepting user input defining a navigation path, robotically navigating the medical device to a starting point on the path, and robotically navigating the medical device along the navigation path to an endpoint. Waypoints defining the navigation path may be input on a graphical representation of the topography using a user interface such as a pointing device or touchscreen. The navigation path may also be defined by tracing a substantially continuous path on the graphical representation. A therapy may be administered while robotically navigating the medical device along the navigation path, either forward or in reverse, or while navigating the medical device along a return path defined by a plurality of virtual breadcrumbs generated as the medical device traverses the navigation path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No.60/851,042, filed 12 Oct. 2006, which is hereby expressly incorporatedby reference as though fully set forth herein.

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/139,908, filed 27 May 2005 now U.S. Pat. No. 7,632,265 (the'908 application), which claims the benefit of U.S. provisionalapplication No. 60/575,741, filed 28 May 2004 (the '741 application).The '908 and '741 applications are hereby expressly incorporated byreference as though fully set forth herein.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The instant invention relates to robotically controlled medical devices.In particular, the instant invention relates to a robotic surgicalsystem for navigating a medical device through a patient's body fordiagnostic and therapeutic purposes.

b. Background Art

Catheters are used for an ever growing number of medical procedures. Toname just a few examples, catheters are used for diagnostic,therapeutic, and ablation procedures. Typically, the user manuallymanipulates the catheter through the patient's vasculature to theintended site, such as a site within the patient's heart. The cathetertypically carries one or more electrodes or other diagnostic ortherapeutic devices, which may be used for ablation, diagnosis, cardiacmapping, or the like.

It is well known that, to facilitate manipulation of the catheterthrough the patient's vasculature to the intended site, portions of thecatheter shaft, especially the distal regions thereof, may be madesteerable. For example, the catheter may be manufactured such that theuser can translate, rotate, and deflect the distal end of the catheteras necessary and desired to negotiate the tortuous paths of thepatient's vasculature en route to the target site. Navigating a catheterreliably through the patient's body to a precise location, however, isan extremely tedious process requiring a substantial amount of time andskill and potentially causing a high degree of fatigue in the physician,especially where actuation forces are transmitted over large distances.

BRIEF SUMMARY OF THE INVENTION

It is thus desirable to be able to navigate a medical device accuratelyand precisely through a patient's body to the locations of diagnostic ortherapeutic interest.

It is also desirable to be able to reduce the fatigue factor associatedwith navigating a medical device through a patient's body.

It is further desirable to be able to preserve the ability to manuallynavigate a medical device when so desired.

It is also desirable that the medical device be able to distinguishproximity or degree of contact between the medical device and a tissuesurface.

It is further desirable that the medical device be usable to create amap of a geometry of the patient's body, which map may includediagnostic information, without the need to distinguish surface pointsfrom interior points during the data-gathering phase.

Still further, it is desirable to equip the robotic control system tonavigate the catheter according to a predetermined path in order toautomatically deliver a therapy, such as a tissue ablation, or perform adiagnostic procedure.

According to a first aspect of the invention, a method of navigating amedical device through a body of a patient includes: providing atopography of at least a portion of the body; accepting user inputdefining a navigation path including a plurality of waypoints on thetopography, the plurality of waypoints including a first waypoint and afinal waypoint; robotically navigating the medical device to the firstwaypoint; and robotically navigating the medical device along thenavigation path from the first waypoint to the final waypoint.Optionally, the method includes administering a therapy with the medicaldevice, for example ablating tissue or delivering a therapeutic agent,while robotically navigating the medical device along the navigationpath either going forward or in reverse. Reverse navigation may beaccomplished by recording in a memory device a plurality of roboticsettings, the plurality of robotic settings corresponding to roboticsettings that were used to robotically place the medical device at eachof the plurality of waypoints that define the navigation path, andutilizing the plurality of recorded robotic settings to improve accuracyof travel of the medical device along the navigation path in reverse.The therapy may alternatively be administered while roboticallynavigating the medical device along a return path from the finalwaypoint to the first waypoint. The return path may include a pluralityof reference points generated by periodically measuring a position ofthe medical device while navigating the medical device along thenavigation path from the first waypoint to the final waypoint. Asampling rate for periodically measuring a position of the medicaldevice may be adjustable, and may be user adjustable. Alternatively, aresolution of the return path may be user-adjustable. Optionally, thestep of providing a topography of at least a portion of the bodyincludes providing a graphical representation of the topography througha user interface, and the step of accepting user input defining anavigation path including a plurality of waypoints on the topographyincludes accepting user input defining the plurality of waypoints on thegraphical representation through the user interface. User input definingthe plurality of waypoints on the graphical representation may beaccepted user input through a pointing device or a touchscreen. Themedical device may be robotically navigated along the navigation pathfrom the first waypoint to the final waypoint while maintaining contactbetween the medical device and a tissue surface, which may include:measuring a contact force between the medical device and the tissuesurface; and robotically actuating the medical device to maintain thecontact force between the medical device and the tissue surface at asubstantially constant level.

According to another aspect of the invention, a method of automaticallydelivering a treatment to a heart of a patient includes the steps of:displaying an anatomical model of at least a portion of the heart;accepting user input designating a treatment pathway on the anatomicalmodel, the treatment pathway including at least a starting point and anendpoint; automatically actuating a therapeutic device control system toadvance a therapeutic device into contact with a cardiac surface at thestarting point; and automatically actuating the therapeutic devicecontrol system to navigate the therapeutic device along the treatmentpathway from the starting point to the endpoint while maintainingcontact between the therapeutic device and the cardiac surface. The stepof accepting user input designating a treatment pathway may includeaccepting user input from one or more of a touchpad, a trackball, amouse, a joystick, and a touchscreen. The starting point and theendpoint may be substantially co-located such that the treatment pathwayis a substantially closed loop. The treatment pathway optionallyincludes a plurality of waypoints, including the starting point and theendpoint. Alternatively, the treatment pathway may be tracedsubstantially continuously on the anatomical model. Since the cardiacsurface may be moving due to beating of the heart, the step ofautomatically actuating a therapeutic device control system to advance atherapeutic device into contact with a cardiac surface at the startingpoint may include: automatically actuating the therapeutic devicecontrol system to advance the therapeutic device to a position proximatethe starting point; periodically sensing for contact between thetherapeutic device and the moving cardiac surface; and upon sensingcontact with the moving cardiac surface, synchronizing automaticactuation of the therapeutic device control system with motion of themoving cardiac surface in order to maintain contact between thetherapeutic device and the moving cardiac surface. The step ofsynchronizing automatic actuation of the therapeutic device controlsystem with motion of the moving cardiac surface optionally includesperiodically measuring a contact force between the therapeutic deviceand the moving cardiac surface and automatically actuating thetherapeutic device control system to maintain the contact force betweenthe therapeutic device and the cardiac surface within a predeterminedrange of contact forces. Automatically actuating the therapeutic devicecontrol system to maintain the contact force between the therapeuticdevice and the cardiac surface within a predetermined range of contactforces may include automatically actuating the therapeutic devicecontrol system to advance the therapeutic device relative to the cardiacsurface when a rate of change in the contact force is indicative of thecardiac surface moving away from the therapeutic device andautomatically actuating the therapeutic device control system to retractthe therapeutic device relative to the cardiac surface when a rate ofchange in the contact force is indicative of the cardiac surface movingtowards the therapeutic device. The method optionally includes utilizingthe therapeutic device to deliver a treatment to at least one targetpoint along the treatment pathway. The therapy may be deliveredsubstantially continuously along at least a portion of the treatmentpathway. The therapeutic device may also be automatically actuated tonavigate along a return path from the endpoint to the starting point,and a therapy may be administered while navigating along the returnpath.

In another embodiment of the invention, a therapeutic device controlsystem includes: a servo-driven therapeutic device manipulation system,said manipulation system having at least three degrees of freedom; atleast one therapeutic device carried by the manipulation system; a userinterface including an input device that permits a user to define aplurality of target points on a tissue surface; and a controller foractuating the manipulation system to navigate the at least onetherapeutic device to at least one target point of the plurality oftarget points. The controller optionally includes software forautomatically actuating the manipulation system to navigate the at leastone therapeutic device to the at least one target point. A positionalfeedback system may be provided for determining a location of the atleast one therapeutic device, and the controller may utilize informationfrom the positional feedback system in actuating the manipulation systemto navigate the at least one therapeutic device to the at least onetarget point. The controller may also include software for automaticallyactuating the manipulation system to maintain contact between the atleast one therapeutic device and the tissue surface. The software forautomatically actuating the manipulation system to maintain contactbetween the at least one therapeutic device and the tissue surface mayinclude software for automatically synchronizing movement of the atleast one therapeutic device to movement of the tissue surface. The userinterface optionally includes a display for presenting a graphical modelof at least a portion of the tissue surface and an input device fordesignating the plurality of target points on the graphical model. Theinput device may be selected from the group consisting of a touchscreen,a joystick, a touchpad, a mouse, and a trackball. In some embodiments,the manipulation system may include three servo motors for manipulatingthe at least one therapeutic device in three degrees of freedom. The atleast one therapeutic device is preferably selected from the groupconsisting of catheters, syringes, electrophoration devices,iontophoresis devices, transdermal pharmaceutical delivery devices,myoblast delivery devices, stem cell delivery devices, ablation devices,pacemaker leads, and any combinations thereof.

In still another embodiment of the invention, a system for defining andnavigating a treatment path within a body of a patient includes: adisplay for presenting a graphical model of at least a portion of thebody of the patient; a user input device for defining the treatment pathon the graphical model of at least a portion of the body and foridentifying at least one treatment location on the treatment path; aservo-driven manipulation system for maneuvering a therapeutic devicewithin the body of the patient; a positional feedback system fordetermining a location of the therapeutic device within the body of thepatient; and a controller for actuating the manipulation system tomaneuver the therapeutic device within the body and along the treatmentpath by utilizing information from the positional feedback system.Optionally, a memory device is provided for storing a plurality ofreference points generated by periodically measuring a position of thetherapeutic device while maneuvering the therapeutic device along thetreatment path. A processor for generating a return path from theplurality of reference points may also be included. The controlleroptionally actuates the manipulation system to maneuver the therapeuticdevice along the return path.

An advantage of the present invention is a reduced exposure to radiationfor both the patient and the physician, since the present inventionreduces the time required to navigate the catheter to a target locationand minimizes the need for fluoroscopy to locate the catheter within thepatient.

Another advantage of the present invention is the ability to easilyswitch between automated robotic control and manual control of thecatheter.

Still another advantage of the present invention is the ability toremotely interact with the robotic surgical system controlling thecatheter.

The foregoing and other aspects, features, details, utilities, andadvantages of the present invention will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an embodiment of a roboticsurgical system.

FIG. 2 is a perspective view of one embodiment of a catheter holdingdevice with a catheter placed therein.

FIG. 3 is an end view of the catheter holding device of FIG. 2.

FIG. 4 is a perspective view of one embodiment of a catheter holdingdevice with a catheter secured therein.

FIG. 5 is an end view of the catheter holding device of FIG. 4.

FIG. 6 illustrates an exemplary steerable catheter such as may be usedin the robotic surgical system.

FIG. 7 depicts automatic control of the robotic surgical systemaccording to a predetermined program.

FIG. 8 depicts a user manually controlling the robotic surgical systemvia an input device.

FIG. 9 depicts the user of FIG. 8 manually controlling the steerablecatheter after having removed it from the robotic surgical system.

FIG. 10 schematically illustrates a contact sensing surgical system.

FIG. 11 is a high-level flowchart of a contact sensing methodology.

FIGS. 12 a through 12 o illustrate alternative implementations of thedecision process for indicating a change in proximity or degree ofcontact in the high-level flowchart of FIG. 11.

FIG. 13 a is an exemplary plot of tissue parameter versus either time orprobe distance as measured by a contact sensing surgical system.

FIG. 13 b is the derivative of the plot in FIG. 13 a.

FIG. 14 illustrates a system for generating a three-dimensional model ofa portion of a patient's body, optionally including diagnosticinformation.

FIG. 15 illustrates a graphical representation of a three-dimensionalmodel of a heart chamber including diagnostic information superimposedthereon.

FIG. 16 illustrates the definition of a navigation path on a graphicalrepresentation of a model of a heart chamber.

DETAILED DESCRIPTION OF THE INVENTION

Robotic Surgical System

FIG. 1 schematically illustrates an embodiment of a robotic surgicalsystem 10 for robotic manipulation and control of a medical device 12.Medical device 12 is preferably a catheter, which may be any type ofcatheter, including, by way of example only and without limitation, anablation catheter, a guide wire catheter, an introducer catheter, aprobe, or a stylet. It should be understood, however, that any othertherapeutic, diagnostic, or assistive medical device may be controlledby robotic surgical system 10 without departing from the scope of thepresent invention. Such other devices include, but are not limited to,syringes, electrophoresis devices, iontophoresis devices, transdermalpharmaceutical delivery devices, myoblast delivery devices, stem celldelivery devices, ablation devices, stents, and pacemaker leads, whichmay be carried on or delivered by a catheter. It should further beunderstood that robotic surgical system 10 may be used to manipulate andcontrol more than one medical device 12 in accordance with the quickinstallation and removal feature described herein. Accordingly, theterms “medical device,” “probe,” “therapeutic device,” and “catheter”are used interchangeably herein.

Robotic surgical system 10 generally includes a track 14, a catheterholding device 16, a translation servo mechanism 18, a catheterdeflection control mechanism 20, a deflection servo mechanism 22, and acontroller 24 operatively coupled to at least one of translation servomechanism 18 and deflection servo mechanism 22. Translation anddeflection servo mechanisms 18, 22 may be any type of device forproviding mechanical control at a distance, including continuous motors,stepper motors, hydraulic actuators, pulley systems, and other devicesknown to those of ordinary skill in the art. Catheter deflection controlmechanism 20 and deflection servo mechanism 22 are collectively referredto herein as a “catheter deflection mechanism.”

Catheter holding device 16 includes a catheter receiving portion 26.Catheter receiving portion 26 is configured to receive catheter 12 byinstalling a catheter control handle 28, located near a proximal end 30of catheter 12, into catheter receiving portion 26. Preferably, catheterreceiving portion 26 is adapted for quick installation and removal ofany type of catheter 12 (or, as noted above, another medical device),thereby facilitating the installation of device 12 for control byrobotic surgical system 10 and removal of device 12 for manual control(e.g., user manipulation of catheter control handle 28). Accordingly,catheter control handle 28 may be secured in catheter receiving portion26 by a frictional fit or with one or more quick-release fasteners.Alternatively, the inner surface of catheter receiving portion 26 andthe outer surface of catheter control handle 28 may include matingthreaded portions to permit catheter control handle 28 to be screwedinto catheter holding device 16. In other embodiments of roboticsurgical system 10, catheter control handle 28 is clamped or strapped inplace in catheter receiving portion 26. An adapter may also be used tofacilitate the reception of catheter control handle 28 within catheterreceiving portion 26.

One embodiment of catheter holding device 16 is illustrated in FIGS. 2and 3 with catheter control handle 28 placed, but not secured, therein.Catheter holding device 16 includes a base plate 32 and a plurality ofupstanding support plates 34. Support plates 34 support cams 36, whichare connected to pulley systems 38.

Catheter control handle 28 is received downwardly through an opening 40into the catheter receiving portion 26 and onto belts 40 of pulleysystems 38. As catheter control handle is urged downwardly, belts 40rotate upper and lower pulleys 38 a, 38 b in the direction of arrows a.This, in turn, urges cams 36 downwards via links 42 and draws upperpulleys 38 a, 38 b towards one another via links 44, whilesimultaneously wrapping the belts 40 about catheter control handle 28.Catheter control handle 28 is thereby secured within catheter receivingportion 26 as shown in FIGS. 4 and 5. To remove catheter control handle28 from catheter holding device 16, the user need only release cams 26,which reverses the process described above and opens catheter receivingportion 26.

Catheter holding device 16 is translatably associated with track 14. Thephrase “translatably associated with” encompasses all types of relativelateral motion between catheter holding device 16 and track 14. Forexample, catheter holding device 16 may slide relative to track 14.Alternatively, catheter holding device 16 may move laterally along ascrew mechanism 46, such as a worm gear, a lead screw, or a ball screw,attached to track 14. Preferably, catheter holding device 16 has atranslation range relative to track 14 (i.e., the lateral distance thatcatheter holding device 16 can travel relative to track 14 betweenextremes) of at least about 5 cm, the approximate width of a humanheart. More preferably, the translation range of catheter holding device16 relative to track 14 is at least about 10 cm.

In the preferred embodiment of the invention, a carriage 48 istranslatably mounted on track 14 via screw mechanism 46. Catheterholding device 16 is mounted on carriage 48 such that catheter holdingdevice 16 translates relative to track 14 with carriage 48. For example,base plate 32 may be fixedly or removably mounted on carriage 48.Alternatively, catheter holding device 16 may be integrally formed withcarriage 48 as a single assembly (i.e., base plate 32 and carriage 48may be a single, unitary component). Likewise, in some embodiments ofthe invention, catheter holding device 16 may be translatably mounteddirectly on track 14 without an intervening carriage.

Translation servo mechanism 18 is operatively coupled to catheterholding device 16 and adapted to control translation of catheter holdingdevice 16 relative to track 14 in order to adjust the lateral positionof catheter holding device 16 along track 14. Preferably, translationservo mechanism 18 is operatively coupled to carriage 48 in order tomove carriage 48, and therefore catheter holding device 16 mountedthereon, laterally along track 14. In the embodiment shown in FIG. 1,translation servo mechanism 18 drives screw mechanism 46, thereby movingcarriage 48 laterally therealong.

Deflection servo mechanism 22 is operatively coupled to and adapted tocontrol catheter deflection control mechanism 20. In the preferredembodiment of the invention, deflection servo mechanism 22 isoperatively coupled to catheter deflection control mechanism 20 suchthat deflection servo mechanism 22 can rotate catheter deflectioncontrol mechanism 20. Either or both of deflection servo mechanism 22and catheter deflection control mechanism 20 may be mounted on carriage48 in order to simplify the transmission system linking deflection servomechanism 22 and catheter deflection control mechanism 20. In someembodiments of robotic surgical system 10, catheter deflection controlmechanism 20 is incorporated in catheter holding device 16, for exampleby utilizing pulley systems 38, and in particular belts 40, as furtherdescribed below. One of ordinary skill in the art will appreciate,however, that catheter deflection control mechanism 20 may also beseparated from catheter holding device 16 without departing from thespirit and scope of the present invention.

Controller 24 is adapted to control at least one of translation servomechanism 18 and deflection servo mechanism 22 in order to navigatecatheter 12 received in catheter holding device 16. It should also benoted that the use of multiple controllers to control translation servomechanism 18 and deflection servo mechanism 22 is regarded as within thescope of the present invention. Throughout this disclosure, the term“controller” refers to a device that controls the movement or actuationof one or more robotic systems (that is, the component responsible forproviding command inputs to the servo mechanisms). One of ordinary skillin the art will understand how to select an appropriate controller forany particular mechanism within robotic surgical system 10. Further, theterm “controller” should be regarded as encompassing both a singular,integrated controller and a plurality of controllers for actuating oneor more robotic systems.

As shown in FIG. 6, catheter 12 is preferably a steerable catheterincluding at least one pull wire 50 extending from catheter controlhandle 28 near proximal end 30 of catheter 12 to a distal end 52 ofcatheter 12. Pull wires 50 may be coupled to at least one pull ring 54,also located near distal end 52 of catheter 12. When placed in tension,pull wires 50 deflect distal end 52 of catheter 12 into variousconfigurations. As one of skill in the art will understand, additionalpull wires 50 will enhance the deflection versatility of distal end 52of catheter 12. For example, a single pull wire 50 with a single pointof attachment to pull ring 54 will permit distal end 52 of catheter 12to deflect on a single axis, and perhaps in only one direction, forexample upwards relative to FIG. 6. By adding a second pull wire 50 (asshown in FIG. 6), or by looping a single pull wire 50 to have two pointsof attachment 56 to pull ring 54, distal end 52 of catheter 12 may bedeflected in two directions, for example both upwards and downwardsrelative to FIG. 6. A catheter 12 with four pull wires 50 attached topull ring 54 at about 90° intervals can deflect in four directions, forexample upwards, downwards, and into and out of the plane of the paperrelative to FIG. 6.

One or more catheter deflection actuators 58 may be provided on cathetercontrol handle 28 to selectively tension one or more pull wires 50,thereby controlling the direction and degree of deflection of distal end52 of catheter 12. In some embodiments, one or more knobs may beprovided, rotation of which selectively tension one or more pull wires50. It should be understood, however, that catheter deflection actuators58 may take many other forms, including, but not limited to, sliders andswitches, without departing from the spirit and scope of the presentinvention. Additionally, it is contemplated that rotating cathetercontrol handle 28 itself may selectively tension pull wires 50 anddeflect distal end 52 of catheter 12.

Returning to FIG. 1, when catheter control handle 28 is received withincatheter receiving portion 26, catheter 12 translates relative to track14 with catheter holding device 16, thereby providing a first degree offreedom permitting catheter 12 to be advanced into and retracted from apatient's body. Additionally, catheter 12 is operatively coupled tocatheter deflection control mechanism 20 such that actuation of catheterdeflection control mechanism 20 causes distal end 52 of catheter 12 todeflect, thereby providing a second degree of freedom to catheter 12. Inparticular, catheter deflection actuator 58 may be operatively coupledto catheter deflection control mechanism 20 such that catheterdeflection control mechanism 20 can actuate catheter deflection actuator58 to selectively tension one or more pull wires 50 and deflect thedistal end 52 of catheter 12 by a desired amount in a desired direction.

In some embodiments of the invention, rotating catheter deflectioncontrol mechanism 20 will rotate catheter deflection actuator 58 inturn, thereby selectively tensioning one or more pull wires 50 withincatheter 12. The transmission system between catheter deflection controlmechanism 20 and catheter deflection actuator 58 may be a frictional fitprovided, for example, by rubberized coatings surrounding catheterdeflection control mechanism 20 and catheter deflection actuator 58.Alternatively, catheter deflection control mechanism 20 and catheterdeflection actuator 58 may be coupled with mating gear teeth orknurling.

Referring specifically to the embodiment of catheter holding device 16depicted in FIGS. 2-5, when catheter 12 is secured in catheter receivingportion 26, belts 40 frictionally engage catheter control handle 28.They may also engage catheter deflection actuator 58. Thus, if pulleysystem 38 is driven by deflection servo mechanism 22, belts 40 mayrotate catheter control handle 28, catheter deflection actuator 58, orboth, in order to selectively tension one or more pull wires 50 anddeflect distal end 52 of catheter 12.

It should be understood that the particular configurations of catheterdeflection control mechanism 20 and catheter deflection actuator 58described above are merely exemplary and can be modified withoutdeparting from the spirit and scope of the invention. For example, ifcatheter deflection actuator 58 is a slider rather than a knob, catheterdeflection control mechanism 20 may be suitably modified, or evenreplaced as a modular unit, to actuate a slider. This facilitates thequick connect/disconnect operation of robotic surgical system 10 byallowing easy installation and interconnection between off-the-shelfmedical devices of varying construction and robotic surgical system 10.

As described above, the inclusion of additional pull wires 50 incatheter 12 increases the number of directions in which distal end 52 ofcatheter 12 can deflect. This is referred to herein as “deflectionversatility.” Where relatively few pull wires 50 (e.g., fewer than aboutfour pull wires 50) are used, however, compensation for lost deflectionversatility may be had by rotating catheter 12 about its axis. Forexample, in a catheter using only a single pull wire 50 with a singlepoint of attachment to pull ring 54, permitting the catheter to deflectonly in one direction, the catheter may be deflected in the oppositedirection simply by rotating it 180° about its axis. Similarly, acatheter that can deflect in two directions 180° apart can be deflectedin the directions midway therebetween by rotating the catheter 90° aboutits axis.

Accordingly, in some embodiments of the invention, catheter receivingportion 26 is rotatable. An example of such a rotatable catheterreceiving portion is catheter receiving portion 26 defined by pulleysystem 38 depicted in FIGS. 2-5. A rotation servo mechanism 60 isoperatively coupled to rotatable catheter receiving portion 26 andadapted to control rotatable catheter receiving portion 26. Thus, pulleysystem 38 may be driven by rotation servo mechanism 60, thereby engagingbelts 40 to rotate catheter 12 about its axis.

If desired, rotation servo mechanism 60 may be mounted on carriage 48 oraffixed to catheter holding device 16 such that rotation servo mechanism60 translates relative to track 14 with catheter holding device 16. Thisarrangement creates a fixed-distance relationship between rotation servomechanism 60 and catheter holding device 16, which can simplify thetransmission system coupling rotation servo mechanism 60 to catheterholding device 16.

When installed in catheter holding device 16, catheter 12 rotates withcatheter receiving portion 26, thereby providing a third degree offreedom to catheter 12 and compensating for low deflection versatilityattributable to a relatively lower number of pull wires 50. Catheterreceiving portion 26 is preferably rotatable at least about 360° aboutits axis, such that catheter 12 received therein is also rotatable atleast about 360° about its axis, thereby facilitating deflection ofdistal end 52 of catheter 12 in substantially any direction,significantly enhancing the deflection versatility of the distal end 52of the catheter 12. Catheter receiving portion 26 may also be designedto rotate about 720° or more about its axis.

Rotating catheter 12 by rotating catheter receiving portion 26 may causeinadvertent deflection of distal end 52 of catheter 12. As one skilledin the art will recognize from this disclosure, as catheter receivingportion 26 and catheter 12 rotate, catheter deflection actuator 58 mayremain stationary, rather than rotating with catheter control handle 28,if the torque applied by rotation servo mechanism 60 is insufficient toovercome the inertia of catheter deflection control mechanism 20. Thatis, catheter deflection actuator 58 may bind against catheter deflectioncontrol mechanism 20, causing relative rotation between catheter controlhandle 28 and catheter deflection actuator 58. This relative rotationmay result in uncommanded tensioning of one or more pull wires 50,inadvertently deflecting distal end 52 of catheter 12.

To maintain a substantially constant deflection as catheter 12 rotates,therefore, controller 24 may be operatively coupled to both rotationservo mechanism 60 and deflection servo mechanism 22. Controller 24 isadapted to control at least one of deflection servo mechanism 22 androtation servo mechanism 60, and preferably to simultaneously controlboth deflection servo mechanism 22 and rotation servo mechanism 60, tomaintain a substantially constant deflection of distal end 52 ascatheter receiving portion 26 and catheter 12 rotate. For example, ascontroller 24 commands rotation servo mechanism 60 to rotate catheterreceiving portion 26, controller 24 may simultaneously commanddeflection servo mechanism 22 to actuate catheter deflection controlmechanism 20 to counter-rotate, thereby substantially eliminatingrelative rotation between the catheter deflection actuator 58 andcatheter control handle 28, helping to maintain a substantially constantdeflection of catheter 12. Alternatively, as controller 24 commandsrotation servo mechanism 60 to rotate catheter receiving portion 26, itmay simultaneously command deflection servo mechanism 22 to decouplecatheter deflection control mechanism 20 from catheter deflectionactuator 58, thereby permitting catheter deflection actuator 58 torotate freely with catheter control handle 28. In either case,controller 24 may be configured to eliminate the need to coupledeflection servo mechanism 22 and rotation servo mechanism 60 through amechanical transmission system such as a differential. Further, thoughdescribed herein as a single controller adapted to control thetranslation, deflection, and rotation servo mechanisms 18, 22, 60,multiple controllers may be used without departing from the spirit andscope of the present invention.

An introducer 62, preferably a steerable introducer, and most preferablyan Agilis™ steerable introducer, may be provided as part of roboticsurgical system 10. A proximal end 64 of introducer 62 is preferablystationary, while a distal end 66 of introducer 62 extends into apatient (not shown for clarity) to a location proximate a target site(the term “target” is used herein to refer to a location at whichtreatment or diagnosis occurs). Introducer 62 may be steerable via arobotic control system 68 including at least one servo mechanism 70adapted to control distal end 66 of introducer 62 in at least one degreeof freedom. Preferably, robotic control system 68 includes three servomechanisms 70 adapted to control distal end 66 of the introducer 62 inthree degrees of freedom (translation, deflection, and rotation),resulting in a total of six degrees of freedom for robotic surgicalsystem 10, and at least one controller 72 adapted to control servomechanisms 70. Similar control principles may be applied to steerableintroducer 62 as are described herein with respect to robotic surgicalsystem 10 and medical device 12.

One of ordinary skill in the art will appreciate that the deflection ofdistal end 52 of catheter 12 is a function not only of the input tocatheter deflection actuator 58 (i.e., the selective tensioning of oneor more pull wires 50), but also of the extent to which catheter 12 isadvanced beyond a generally rigid sheath, such as introducer 62. Thatis, the further distal end 52 of catheter 12 is advanced beyond distalend 66 of introducer 62, the greater the deflection of distal end 52 ofcatheter 12 will be for a given input at catheter deflection actuator58.

It is therefore desirable to calibrate the deflection of distal end 52of catheter 12 in terms of both catheter deflection control mechanisminputs and extensions of catheter 12 beyond distal end 66 of introducer62. By robotically actuating catheter deflection control mechanism 20between extremes (e.g., commanding a complete rotation of catheterdeflection actuator 58) and measuring the resulting deflection of distalend 52 of catheter 12 (e.g., using a localization system), catheterdeflection control mechanism inputs may be correlated with deflectionsof distal end 52 for a given extension of catheter 12 beyond distal end66 of introducer 62. A similar process may be performed for a multipledifferent extensions of catheter 12 beyond distal end 66 of introducer62, resulting in a family of calibration curves relating catheterdeflection control mechanism inputs to deflections of distal end 52 ofcatheter 12. Each curve corresponds to a particular extension ofcatheter 12 beyond distal end 66 of introducer 62; the amount ofextension of catheter 12 beyond distal end 66 of introducer 62 may bederived, at least in part, from the amount of translation of catheterholding device 16 relative to track 14.

To create a substantially sterile field around catheter 12 outside thepatient's body, an expandable and collapsible tubular shaft 74substantially surrounds at least a portion of catheter 12, such as theregion of catheter 12 between catheter holding device 16 and proximalend 64 of introducer 62. Preferably, shaft 74 is sterilized before usealong with other relevant components of robotic surgical system 10. Ascatheter holding device 16 translates to advance catheter 12 into thepatient (i.e., to the right in FIG. 1), tubular shaft 74 collapses uponitself. Contrarily, as catheter holding device 16 translates to retractcatheter 12 from the patient (i.e., to the left in FIG. 1), tubularshaft 74 expands. Preferably, tubular shaft 74 is assembled from aplurality of telescoping tubular elements 76. It is contemplated,however, that tubular shaft 74 may alternatively be an accordion-pleatedor other expandable and collapsible structure.

As depicted in FIGS. 7 and 8, robotic surgical system 10 may be employedto robotically navigate catheter 12 into and through the patient and toone or more sites, which may be target sites, within the patient's bodyby actuating one or more of translation servo mechanism 18, deflectionservo mechanism 22, and rotation servo mechanism 60 (if present) viacontroller 24. Robotic surgical system 10 may operate automaticallyaccording to a computerized program as executed by controller 24 (FIG.7). It is also contemplated that the user, who may be a surgeon,cardiologist, or other physician, may control robotic surgical system 10through an appropriate set of controls 78, such as a three-dimensionaljoystick (e.g., a joystick with three input axes), a steering yoke, oranother suitable input device or collection of such devices permittingthe user to robotically steer catheter 12 (FIG. 8).

As described above, catheter 12 can be quickly and easily disconnectedfrom catheter holding device 16. Thus, if the user desires to manuallycontrol catheter 12 at any point during the procedure, the user maydisconnect catheter 12 from the catheter holding device 16 as describedabove. The user may navigate catheter 12 manually for as long asdesired, and then replace it into catheter holding device 16 and resumerobotic control. FIG. 9 illustrates the user manually operating catheter12 after having removed it from catheter holding device 16.

In some embodiments of the invention, multiple robotic surgical systemscontrolling multiple medical devices may be employed during a procedure.For example, a first robotic surgical system may control an ultrasonicimaging transducer, while a second robotic surgical system may controlan ablation catheter. A single controller, or multiple cooperatingcontrollers, may coordinate the multiple medical devices and themultiple robotic surgical systems, for example in conjunction with asingle localization system, or alternatively by utilizing data from theultrasonic imaging transducer to control the movement of the ablationcatheter.

Robotic surgical system 10 facilitates precise and accurate navigationof medical device 12 within the patient's body. In addition, sincemedical device 12 is manipulated primarily robotically, the physicianwill experience considerably less fatigue during the surgical procedure.Furthermore, robotic control permits a substantially increased degree ofcomplexity in the control and actuation mechanisms that may beincorporated into medical device 12 over those that may be used in amedical device 12 intended solely for human control, enabling anincrease in the versatility of medical device 12.

Contact Sensing

FIG. 10 schematically illustrates a surgical system 80 equipped to sensecontact between a probe, such as catheter 12, and a tissue surface 82,such as a cardiac wall. Probe 12 includes a sensor or instrument 84carried thereon, preferably at distal end 52 of probe 12, for measuringthe value of a parameter (referred to herein as P) of tissue surface 82either periodically (that is, with a relatively fixed interval betweenmeasurements) or episodically (that is, with a variable interval betweenmeasurements). Preferably, sensor 84 is an electrophysiology sensorcapable of measuring one or more electrophysiology characteristics,including, but not limited to, impedance, phase angle, electrogramamplitude, optical feedback, and ultrasonic feedback.

To facilitate precise determination of the distance traveled by probe 12between measurements of the tissue parameter (referred to herein as Δs),a precisely calibrated system is utilized. The precisely calibratedsystem may be a robotically controlled system to move probe 12 withinthe patient's body, such as robotic surgical system 10 described herein.It is also contemplated that measurements of the position of probe 12within the patient's body may be made using a using a precisely locally-or universally-calibrated positional feedback (i.e., localization)system 86 in conjunction with a location or position electrode 88carried on probe 12. Preferably, the positional feedback system is theEnsite NavX™ system of St. Jude Medical, Inc., which includes pairs ofelectrodes 90 defining measurement axes by which the position of probe12 may be measured. One of ordinary skill in the art will appreciatethat other localization systems, such as the CARTO navigation systemfrom Biosense Webster, Inc., may also be employed. Only one pair ofelectrodes 90 is illustrated; one of skill in the art will appreciatethat additional pairs of electrodes 90 may be used if additionalmeasurement axes are desired.

A processor monitors the value of the tissue parameter measured bysensor 84 as probe 12 moves within the patient's body. The processor maybe incorporated in a computer system 92. For purposes of thisdisclosure, a single processor within computer system 92 will bereferred to, though it is contemplated that multiple computer systems 92and/or multiple processors within a single computer system 92 may beused to practice the various aspects of the present invention. Further,one or more processor functions described herein may be integrated in asingle processor without departing from the scope of the presentinvention.

As described above, probe 12 may be moved by a robotically-controlledsystem capable of precise movements on the order of less than about 5mm, more preferably on the order of less than about 2 mm, and mostpreferably on the order of less than about 1 mm. Alternatively, themovements of probe 12 are precisely measured by a positional feedbacksystem 86 with a margin of error of less than about 5 mm, preferablyless than about 2 mm, and more preferably less than about 1 mm. For agiven, precisely determined Δs (e.g., as precisely moved by roboticsurgical system 10 or precisely measured by positional feedback system86), a corresponding amount and rate of change in the tissue parameterbetween measurements can be anticipated for a situation where there isno change in the proximity or degree of contact between probe 12 andtissue surface 82.

The processor monitors the tissue parameter for an indicator ofproximity or degree of contact between probe 12 and tissue surface 82and indicates a change in the proximity or degree of contact betweenprobe 12 and tissue surface 82 based on the monitored tissue parameter.In particular, the processor reports the change in either proximity ordegree of contact based on either the amount of change in the tissueparameter or the rate of change in the tissue parameter betweenmeasurements, and preferably between successive measurements, thereof.The term “proximity” refers to the relationship between probe 12 andtissue surface 82 when probe 12 is not in contact with tissue surface82; it is, in lay terms, a measure of how close probe 12 is to tissuesurface 82. The term “degree of contact” refers to the relationshipbetween probe 12 and tissue surface 82 when probe 12 is in contact withtissue surface 82; it is, in lay terms, a measure of how hard probe 12is pressing into tissue surface 82.

A contact sensing method is illustrated in the high-level flowchart ofFIG. 11. Probe 12 is navigated into the patient's body and intomeaningful proximity with tissue surface 82 in step 100. The term“meaningful proximity” refers to probe 12 being sufficiently close totissue surface 82 such that sensor 84 can capture usefulelectrophysiology information about surface 82, and thus encompassesboth contact and non-contact relationships between probe 12 and tissuesurface 82.

Once inside the patient's body, probe 12 is moved using a calibratedsystem, such as robotic surgical system 10, moved and located using acalibrated system, such as positional feedback system 86, or both. Asprobe 12 moves, the tissue parameter at distal end 52 of probe 12 ismeasured, either periodically or episodically, using sensor 84 (steps102, 104, and 106). An amount of change (ΔP) in the measured tissueparameter between successive measurements (P_(n) and P_(n+1)) iscalculated in step 108. The processor then indicates a change inproximity or degree of contact between probe 12 and tissue surface 82based upon the amount of change in the measured tissue parameter in step110. That is, the processor provides the user and/or controller 24controlling robotic surgical system 10 with an indication of either“change” or “no change” in the proximity or degree of contact based uponthe amount of change in the measured tissue parameter. If desired, theprocess may be repeated as probe 12 continues to move through thepatient's body by setting P_(n)=P_(n+1) (step 112) and moving probe 12to a new location (step 104) where a new P_(n+1) is measured (step 106).

A number of algorithms may be used to identify the change in proximityor degree of contact between probe 12 and tissue surface 82 in step 110.In a first algorithm, illustrated in FIG. 12 a, the amount of change inthe measured tissue parameter (ΔP) is compared to a predetermined rangeof values ranging from a lower limit (LL) to an upper limit (UL) in step114 a. (In FIGS. 12 a through 12 o, absolute values are used in order toaccount for potential negative values of ΔP.) A change is indicated whenthe amount of change in the measured parameter falls outside thepredetermined range of values (step 116 a); no change is indicated whenthe amount of change in the measured parameter falls within thepredetermined range of values (step 118 a).

The predetermined range of values (that is, either or both of UL and LL)may be user selectable, and may correspond generally to the anticipatedamount of change in the measured tissue parameter between measurementswhen there is no change in the proximity or degree of contact betweenprobe 12 and tissue surface 82 for a given Δs. “Predetermined” is usedherein to refer to values that are set in advance of applying thecontact sensing algorithm; for example, the values (i.e., UL and LL) maybe based upon a percentage variation in the anticipated change in themeasured tissue parameter, which percentage may also be user selectable.

In other algorithms, the amount of change in the measured tissueparameter is compared to a change threshold, with the change indicationbased upon whether or not the measured tissue parameter crosses thechange threshold. For example, as shown in FIG. 12 b, the changethreshold may correspond generally to the maximum anticipated amount ofchange in the measured tissue parameter between successive measurementsfor a given Δs (ΔP_(MAX)). Thus, no change in proximity or degree ofcontact would be indicated when the amount of change is less than thechange threshold, and a change in proximity or degree of contact wouldbe indicated when the amount of change is greater than the changethreshold. It is also contemplated that the algorithm may be modified asshown in FIG. 12 c, such that the threshold corresponds generally to theminimum anticipated amount of change in the measured tissue parameterbetween successive measurements for a given Δs (ΔP_(MIN)), which wouldreverse the conditions for indicating change or no change in proximityor degree of contact. The change threshold may be user selectable, andmay be calculated as a percentage variation in the anticipated amount ofchange in the measured tissue parameter for a given Δs, which percentagemay itself be user selectable.

In still other algorithms, the change in proximity or degree of contactis indicated based upon a rate of change in the measured tissueparameter with respect to either the time between measurements (ΔP/Δt)or the distance traveled by probe 12 between measurements (ΔP/Δs). Therate of change may also be calculated as a derivative of the measuredtissue parameter with respect to time (dP/dt) or probe distance traveled(dP/ds). The rate of change may be calculated as a first derivative ofthe tissue parameter, a second derivative of the tissue parameter, orany further derivative of the tissue parameter. One of skill in the artwill recognize that any of these variables may be calculated from theamount of change in the measured tissue parameter and the time betweenmeasurements or the precisely determined distance traveled by probe 12between measurements. The decision processes for indicating change inproximity or degree of contact based upon rate of change variables aresubstantially analogous to the algorithms described with respect to theamount of change in the measured tissue parameter (i.e., comparison to apredetermined range of values or comparison to a rate of changethreshold). These alternative algorithms are illustrated in FIGS. 12d-12 o.

FIG. 13 a is a representative chart of the measured tissue parameter asa function of time (t) or probe distance traveled (s), while FIG. 13 billustrates the derivative of the curve of FIG. 13 a. Initially, inregion 120, there is no change in proximity or degree of contact, so Pvaries only slightly. ΔP is thus quite small, so ΔP/Δt, ΔP/Δs, dP/dt,and dP/ds vary slightly about zero (dP/dt and dP/ds are illustrated inFIG. 13 b).

When a change in proximity or degree of contact occurs, such as at point122, P experiences a substantial change in a very short interval of timeor probe distance traveled. ΔP/Δt and ΔP/Δs are thus quite large, andthe curve of FIG. 13 b illustrating the derivative of the measuredtissue parameter exhibits a corresponding spike 124 before returning tovarying slightly about zero in region 126. A second spike 128corresponds to a point 130 where another change in proximity or degreeof contact occurs.

The contact sensing methods described above are useful in monitoring fora change indicative of probe 12 making contact with tissue surface 82, achange indicative of probe 12 breaking contact with tissue surface 82,or a change indicative of a change in the degree of contact betweenprobe 12 and tissue surface 82. In the lattermost case, the method mayprovide an indicator of whether probe 12 is beginning to break contactwith tissue surface 82 or is potentially being traumatically driven intotissue surface 82. This information may be used by the user and/orrobotic surgical system 10 (e.g., controller 24) as feedback to adjustthe movement of probe 12 to maintain a particular degree of contact withtissue surface 82 on an ongoing basis in order to improve the quality orefficiency of the medical treatment. For example, in an ablationprocedure for the treatment of atrial fibrillation, one of ordinaryskill will readily appreciate that a spike in a derivative of the tissueparameter, as shown in FIG. 13 b, may indicate that the ablationcatheter has broken contact with the cardiac surface and is therefore nolonger creating a substantially continuous lesion and that appropriatecorrective action is necessary to bring the ablation catheter back intocontact with the cardiac surface. As another example, in a surfacemodeling procedure, the spike may indicate that the modeling probe hasbroken contact with the surface being modeled such that the collectionof geometry points should be suspended in order to avoid capturingerroneous data.

Surface Modeling

FIG. 14 illustrates a system 150 for generating a three-dimensionalmodel of at least a portion of the patient's body. Though system 150will be described in the context of generating a three-dimensional modelof the patient's heart chamber 152, it should be understood that system150 and the method disclosed herein may also be employed to map thevolume and tissue surface of any internal organ or other portion of thepatient's body in which the user is interested.

Modeling system 150 includes electrode 154 for insertion into a portionof the patient's heart and a controller (once again denoted ascontroller 24, though an additional controller or controllers could beused) for robotically moving electrode 154 within the portion of theheart either randomly, pseudo-randomly, or according to one or morepredetermined patterns. The term “predetermined pattern” is used to meanany pattern that is not random or pseudo-random, whether that pattern iscomputer- or user-dictated. Further, with reference to the phrase“within a portion of a heart,” it should be appreciated that this doesnot refer to the movement of electrode 154 within the tissue itself(which could be traumatic), but rather to the movement of electrode 154within a space that is interior to the patient's body (such as movementwithin the open space that defines heart chamber 152).

Electrode 154 may be a position, location, or mapping electrode, withthe terms being used interchangeably herein. Controller 24 may beincorporated in robotic surgical system 10 described herein, in whichcase electrode 154 may be carried on catheter 12, preferably at or neardistal end 52 of catheter 12 such that electrode 154 may be brought intocontact with tissue surface 82 of heart chamber 152. It is alsocontemplated that electrode 154 may be located more proximally alongcatheter 12, for example adjacent to electrode 88. In the latterconfiguration, the relationship between electrode 154 and distal end 52may be used to derive position information for distal end 52 fromposition information for electrode 154. It should be understood thatcarrying electrode 154 on a non-catheter probe, utilizing an alternativerobotic control system to move electrode 154, and manually movingelectrode 154 are all regarded as within the scope of the invention. Itshould further be understood that the use of both individual andmultiple electrodes to practice the various aspects of the presentinvention is contemplated (i.e., electrode 88 and electrode 154 may bethe same electrode).

Positional feedback system 86 detects position information of electrode154 within heart chamber 152. Position detector 86 preferably includes aplurality of paired electrodes 90 defining measurement axes for locatingelectrode 154 within the patient's body by utilizing the electricalpotentials measured by electrode 154. An example of a suitablepositional feedback system 86 is disclosed in U.S. application Ser. No.11/227,006, filed 15 Sep. 2005 (the '006 application) and U.S.provisional application No. 60/800,848, filed 17 May 2006 (the '848application), both of which are hereby expressly incorporated byreference as though fully set forth herein. The terms “positiondetector,” “positional feedback system,” “mapping system,” and“navigation system” are used interchangeably herein.

By detecting the position of electrode 154 multiple times as electrode154 is moved within heart chamber 152, position detector 86 generates aplurality, or cloud, of location points defining the space occupied byheart chamber 152. Positional feedback system 86 need not determinewhether a particular location point is a surface point or an interiorpoint during the position detection step; the interior points will beresolved during subsequent processing. That is, the cloud of locationpoints is generated indiscriminately, advantageously reducing theoverhead and time required to collect the data set from which thethree-dimensional model is generated. Thus, the cloud of location pointspreferably includes at least some location points on the surface ofheart chamber 152 (“surface points”) and at least some location pointsnot on the surface of heart chamber 152 (“interior points”). The cloudof location points may be stored in a storage medium, such as a harddrive or random access memory (RAM), which may be part of computersystem 92.

A modeling processor, which may be part of computer system 92, generatesa three-dimensional model of heart chamber 152 from the cloud oflocation points. The three-dimensional model includes positioninformation for a plurality of surface points describing athree-dimensional surface model of heart chamber 152. That is, after thecloud of location points is generated, the modeling processoridentifies, isolates, and either disregards or eliminates the interiorpoints by applying a surface construction or surface modeling algorithmto the plurality of location points. Preferably, the surface modelingalgorithm employed is a shrink-wrap algorithm, though numerous othersurface modeling algorithms are contemplated, including, but not limitedto, convex hull algorithms (e.g., Qhull), alpha shapes, Hoppe'ssoftware, CoCone, and Paraform. The three-dimensional surface model mayoptionally be output as a graphical representation of heart chamber 152on a display 154, which may also be part of computer system 92, oranother output device. Further, the three-dimensional surface model mayoptionally be stored in a storage medium.

In use, electrode 154 is inserted within heart chamber 152, for exampleby advancing electrode 154 into heart chamber 152 on catheter 12controlled by robotic surgical system 10. Next, electrode 154 isrobotically moved within heart chamber 152. As described above, movementof electrode 154 within heart chamber 152 may be random, pseudo-random,or according to a predetermined pattern. Optionally, the predeterminedpattern may include two distinct components: a first predeterminedpattern until a determination is made that electrode 154 is in contactwith tissue surface 82 of heart chamber 152, and a second predeterminedpattern after electrode 154 has made contact with surface 82 of heartchamber 152. The contact sensing methodology described herein may beemployed to determine when electrode 154 has made contact with surface82 of heart chamber 152; to this end, it is contemplated that electrode154 may function as sensor 84. The second predetermined pattern need notbe substantially continuous along surface 82 of heart chamber 152; thatis, electrode 154 may occasionally break contact with surface 82 ofheart chamber 152 while following the second predetermined pattern suchthat electrode 154 “bounces” rather than “skates” along surface 82 ofheart chamber 152.

For example, in some embodiments of the invention, electrode 154 mayfirst measure a few initial location points in a region of heart chamber152. Electrode 154 may then incrementally approach surface 82 of heartchamber 152; the contact sensing methodology described herein, oranother suitable contact sensing methodology, may be utilized todetermine when electrode 154 has contacted surface 82. A location pointmay be collected from surface 82 of heart chamber 152. A section of amodel of surface 82 of heart chamber 152 may then be constructed fromthe initial location points and the surface location point, andelectrode 154 may then be moved small distances, such as about 5 mmanti-normal to surface 82 and about 5 mm laterally to an unsampledregion. This process may then be repeated as necessary to complete thecloud of location points.

As electrode 154 is moved within heart chamber 152, position informationof electrode 154 is detected in order to generate the plurality oflocation points defining the space occupied by heart chamber 152. Ifelectrode 154 is located at or near distal end 52 of catheter 12,position information may be stored directly; if electrode 154 is locatedmore proximally, position information may be derived from therelationship between electrode 154 and distal end 52 prior to beingstored. Detection of position information may be periodic (that is, witha relatively constant interval between successive measurements) orepisodic (that is, with a variable interval between successivemeasurements). Detection may also be event-driven (for example, uponsensing a particular electrophysiological characteristic with sensor84).

The three-dimensional model of heart chamber 152 is then generated fromthe plurality of location points by utilizing a surface constructionalgorithm, such as a shrink-wrap algorithm, to wrap or otherwiseconstruct a surface around the plurality of location points. Thethree-dimensional model includes position information for at least someof the plurality of location points within heart chamber 152, preferablythose location points describing a three-dimensional surface model ofheart chamber 152. The model may be generated by processing theplurality of location points using a surface construction algorithm toidentify and output the subset of the plurality of location pointsdefining the three-dimensional surface model, and thus surface 82 ofheart chamber 152. Interior points may be eliminated or simplydisregarded by the surface construction algorithm. The subset oflocation points may define vertices for a plurality of trianglesrepresenting the three-dimensional surface model of heart chamber 152,and the triangles themselves may be generated by interconnecting thevertices. Once generated, the three-dimensional model may be presentedas a graphical representation on display 156, permitting the user tointeract intuitively with the model through input devices 158, which mayinclude, but are not limited to, a mouse, trackball or other pointingdevice 160; a two- or three-dimensional joystick or control yoke 162;and a keyboard or keypad 164. Input devices 158 may be coupled tocomputer system 92. Optionally, one or more of input devices 158 mayalso serve as controls 78 permitting the user to robotically steercatheter 12.

As one of ordinary skill in the art will understand from the foregoingdescription, the present invention facilitates improved collection oflocation points. For example, manually controlled catheters may tend tofollow repetitive or stereotypical patterns during sampling, and thusmay not collection location points throughout the volume of the heartchamber. The robotically-controlled catheter of the present invention,however, is less susceptible to this shortcoming, in that it is capableof achieving the necessary control vectors to reach substantially all ofthe volume of the heart chamber. Further, the robotically-controlledcatheter may be programmed to avoid repeat sampling of regions or toexclude repeatedly sampled location points, in the event that it isnecessary to travel through a particular region more than once. As aresult, the not only may the plurality of location points be improved,but also the time required to create the three-dimensional model may bereduced.

Diagnostic Data Mapping

Modeling system 150 may also be utilized to generate a diagnosis map forsurface 82 of heart chamber 152 through the addition of an instrumentfor measuring physiological information, and preferably an instrumentfor measuring electrophysiology information, such as sensor 84. Itshould be understood that, though described herein as separatecomponents, one or more of sensor 84, electrode 88, and electrode 154may optionally be combined into a single component carried on probe 12.Sensor 84 measures electrophysiology information at a point on surface82 of heart chamber 152 that is in meaningful proximity to probe 12. Thediagnosis map contains information about the physiologicalcharacteristics of surface 82, for example the tissue impedance atvarious locations on surface 82.

As described above, controller 24 moves probe 12 to a plurality oflocations within heart chamber 152, including into meaningful proximitywith a plurality of surface points. A contact sensor, such as a forcetransducer, or the contact sensing methodology disclosed herein, may beemployed to identify proximity or degree of contact between probe 12 andsurface 82 of heart chamber 152, though, as one of ordinary skill in theart will appreciate, contact sensing is not necessary if the geometry ofheart chamber 152 is already known, since proximity and contactinformation between probe 12 and surface 82 can be derived from theknown geometry and positional feedback system 86.

Preferably, a processor, which may be part of computer system 92, causesprobe 12 to automatically move into meaningful proximity with aplurality of surface points, for example by providing instructions tocontroller 24 incorporated in robotic surgical system 10 to actuate oneor more of servo mechanisms 18, 22, 60 to translate, deflect, and/orrotate probe 12. It is also contemplated that the user may roboticallysteer probe 12 to the plurality of points via a suitable input device158, such as joystick 162.

Sensor 84 detects electrophysiological information for at least some ofthe surface points, and preferably for each surface point. The processorassociates the measured electrophysiological information with theposition information for the surface point at which it was measured. Asone of skill in the art should appreciate from this disclosure, theposition information may be already known (e.g., through application ofthe surface modeling methodology disclosed herein) or may be gatheredconcurrently with the detection of electrophysiological information.Once position and electrophysiological information for the plurality ofsurface points has been gathered and associated as a plurality ofsurface diagnostic data points, the processor generates the diagnosismap of heart chamber 152 therefrom.

The diagnosis map may optionally be combined with the three-dimensionalsurface model of heart chamber 152 generated by the modeling processoror with another model of heart chamber 152 (e.g., an MRI- orCT-generated model). For example, the diagnosis map may be superimposedupon the three-dimensional surface model. If desired, the resultantthree-dimensional diagnosis model, including both position informationand physiological information, can be output on display 156 as agraphical representation. In addition, the diagnosis map orthree-dimensional diagnosis model may be stored in a storage medium,which, as noted above, may be part of computer system 92.

An electrophysiology processor, which also may be incorporated withincomputer system 92, processes the measured electrophysiology informationin order to identify one or more surface points that are potentialtreatment sites. By way of example only, the electrophysiology processormay identify surface points having abnormal impedance as potentialtargets for tissue ablation in the diagnosis and treatment of cardiacarrhythmia. The electrophysiology processor may be coupled to display156 such that the one or more identified potential treatment sites, orother indicia of the measured physiological or electrophysiologicalinformation, may be presented to the user by superimposition on thegraphical representation of the three-dimensional model. For example,the potential treatment sites may be flagged on display 156 with aspecial icon or coloration. Alternatively, contour lines may be added tothe graphical representation to illustrate the physiological and/orelectrophysiological data included in the diagnosis map. FIG. 15illustrates a graphical representation of heart chamber 152 includingboth flagged potential treatment sites 168 and contour lines 170.

The user may employ a user interface 166, including display 156 andinput devices 158, to select one or more of the identified potentialtreatment sites as target points (also referred to herein as “treatmentpoints”), for example by pointing to and clicking on the treatment siteas superimposed on the graphical representation. In order to permit theuser to intuitively designate target points, display 156 may be atouchscreen. User interface 166 is preferably coupled to controller 24,and thus to probe 12, such that, upon selecting one or more targetpoints with user interface 166, controller 24 may cause probe 12 to berelocated thereto for further diagnosis (e.g., the collection ofadditional electrophysiology information at the target site) ortreatment (e.g., the delivery of a therapeutic compound or ablativeenergy to the target site). It is also contemplated that controller 24may operate to automatically navigate probe 12 to one or more identifiedpotential treatment sites for further diagnosis or treatment withoutintervention or target point selection by the user (i.e., controller 24may be responsive directly to the electrophysiology processor).

In use, electrode 154, which is preferably mounted on medical device 12,is inserted within heart chamber 152. (Recall that this term does notembrace embedding electrode 154 in cardiac tissue.) Robotic controller24 is used to move electrode 154 within heart chamber 152 eitherrandomly, pseudo-randomly, or according to one or more predeterminedpatterns, and into meaningful proximity with a plurality of surfacepoints on tissue surface 82 of heart chamber 152 in order to measureelectrophysiology information thereat.

Assuming a known geometry of heart chamber 152, for example as generatedby the surface modeling methodology disclosed herein, electrophysiologyinformation is measured and associated with the pre-existing positioninformation for a plurality of surface points. If the geometry isunknown, the diagnosis mapping and surface modeling processes may becombined such that, as electrode 154 moves within heart chamber 152,both position information and electrophysiology information aremeasured, thereby simultaneously generating a plurality of locationpoints defining the space occupied by heart chamber 152, at least someof which are surface points, and electrophysiology information for thosesurface points. The plurality of location points may be processed asdescribed herein or according to another surface construction algorithmto generate the three-dimensional surface model of heart chamber 152.The measured electrophysiology information is associated with theposition information for at least some of the plurality of surfacepoints in order to generate the diagnosis map. It is also contemplatedthat electrophysiology measurements may be taken after generating theplurality of location points, rather than simultaneously therewith, andeither before or after applying the surface construction algorithm togenerate the surface model.

The diagnosis map can be generated from the resulting plurality ofsurface diagnostic data points. The plurality of surface diagnostic datapoints may also be used to generate a three-dimensional surface model ofheart chamber 152 including both position and electrophysiologyinformation for the plurality of surface points. The diagnosis mapand/or surface model may optionally be stored in a storage medium,either individually or as a composite, or presented as a graphicalrepresentation on display 156, either with or without an accompanyingthree-dimensional model of heart chamber 152.

Once the diagnosis map is generated, it may be used as an intuitiveinterface for the user to select one or more target points, for exampleby using an input device 158 to point and click on the graphicalrepresentation of the three-dimensional model of heart chamber 152 withthe diagnosis map superimposed thereon. Medical device 12 maysubsequently be navigated to the target points so selected in order toprovide treatment, such as ablation of tissue, or for further diagnosis,such as making additional electrophysiology measurements. It iscontemplated that the user selecting the one or more target points maybe remote from robotic surgical system 10. For example, an expertphysician in one city may access the three-dimensional model of heartchamber 152 via a computer network, such as the Internet, and select thetarget points, which may then be delivered to robotic surgical system 10in a second city for execution.

Automated Therapy Delivery

Robotic surgical system 10 may be adapted for automated delivery oftherapy, such as ablation of cardiac or other tissue or the delivery ofa therapeutic agent to a cardiac or other tissue surface. As shown inFIG. 16, user interface 166 permits the user to define a navigation path200 (also referred to herein as a “predetermined path” or “treatmentpath”) on tissue surface 82, preferably by utilizing input devices 158to designate navigation path 200 on the graphical representation ofheart chamber 152 shown on display 156. As described above, the user maybe remote from robotic surgical system 10, providing the advantage ofexpert consultation over even long distances during a procedure. Itshould be understood that the graphical representation may or may notinclude physiological information measured by sensor 84 as describedherein; the user may choose whether or not this information is depictedon display 156.

In some embodiments, the user designates a plurality of waypoints 202,including a first waypoint 202 a (i.e., a starting point) and a finalwaypoint 202 b (i.e., an endpoint), on the graphical representation ofheart chamber 152. The first and final waypoints 202 a, 202 b may besubstantially co-located such that navigation path 200 is asubstantially closed loop (e.g., a closed loop around a the pulmonaryveins). Alternatively, the user may utilize input devices 158 to trace asubstantially continuous treatment path 200 on the graphicalrepresentation without defining individual waypoints 200. The user mayfurther identify at least one target point 204 on the navigation pathwhere a therapy is to be administered or a diagnosis is to be performed.The at least one target point 204 may, but need not, correspond to awaypoint 202, and may be input as described herein in connection withthe diagnostic data mapping aspect of the present invention.

Controller 24 actuates robotic surgical system 10 to navigate medicaldevice 12 along the navigation path “inbound” from first waypoint 202 ato final waypoint 202 b, optionally through one or more intermediatewaypoints 202. If the user has designated target points 204, controller24 actuates robotic surgical system 10 to navigate medical device 12thereto. Controller 24 may utilize positional feedback measured bypositional feedback system 86 to navigate medical device 12 and toposition medical device 12 to the at least one treatment or diagnosislocation (i.e., target points 204).

Controller 24 may include software to further refine the navigation ofmedical device 12. For example, controller 24 may include software toautomate navigation of medical device 12. As another example, controller24 may include software to automatically maintain contact betweenmedical device 12 and tissue surface 82, perhaps by automaticallysynchronizing movement of medical device 12 to movement of tissuesurface 82. This will improve the efficiency of therapy delivery alongtreatment path 200 by ensuring that medical device 12 remains in contactwith tissue surface 82 as it moves, rather than bouncing along tissuesurface 82 as the patient's heart beats or the patient breathes. Thecontact sensing methodology disclosed herein may be utilized to maintaincontact between medical device 12 and tissue surface 82.

As one skilled in the art will recognize, advancing (i.e., pushing)medical device 12 into a patient with precision is more difficult thanretracting (i.e., pulling) it from the patient with precision. It maytherefore be desirable to administer treatment or perform a diagnosticprocedure as device 12 is being retracted rather than as device 12 isbeing advanced. Accordingly, a memory device, which, in embodiments, ispart of computer system 92, may store a plurality of reference pointsgenerated by making periodic measurements of the position of medicaldevice 12 as it is navigated along navigation path 200. A processor,which may also be part of computer system 92, generates a return pathfor medical device 12 from the plurality of reference points. Controller24 can actuate robotic surgical system 10 to navigate medical device 12along the return path. In effect, the reference points are used asreverse waypoints, or virtual breadcrumbs, permitting an “outbound”medical device 12 to retrace its steps during retraction from thepatient. Alternatively, the memory device may store a plurality ofrobotic settings or commands used by controller 24 to actuate roboticsurgical system 10 to robotically place medical device 12 at waypoints202 defining navigation path 200. These commands may thereafter beexecuted in reverse to retract medical device 12 from the patient alongnavigation path 200 in reverse. The use of a return path defined by aplurality of reference points or the reversed robotic settings mayimprove the precision of the navigation of medical device 12 as it isretracted, which in turn may improve the quality of the therapydelivered to tissue surface 82 (i.e., by creating a substantiallycontinuous, smooth ablation lesion).

In use, a topography (i.e., a surface model) of at least a portion ofthe patient's body is provided. The topography may be generated asdescribed herein, and may be depicted graphically on display 156, eitherwith or without diagnostic data superimposed thereon. Next, user inputis accepted to define navigation path 200 on the topography as describedabove. User input may be accepted on the graphical representationthrough a pointing device, such as mouse 160 or a trackball, joystick162, a touchpad, or another suitable device. Alternatively, display 156may be a touchscreen permitting more direct interaction with thegraphical representation.

Medical device 12 is then robotically navigated to first waypoint 202 a,preferably by automatically actuating robotic surgical system 10. Fromfirst waypoint 202 a, medical device 12 is robotically actuated to movealong navigation path 200 to final waypoint 202 b. It should beunderstood that navigation path 200 may incorporate one or more otherwaypoints 202 between first waypoint 202 a and final waypoint 202 b.Once final waypoint 202 b is reached, medical device 12 may berobotically navigated along navigation path 200 in reverse, oralternatively navigated along a return path from final waypoint 202 b tofirst waypoint 202 a, for withdrawal from the patient.

As described above, the return path may be created by periodicallymeasuring a position of medical device 12 as it is navigated alongnavigation path 200 from first waypoint 202 a to final waypoint 202 b.These periodic measurements become reference points, which may bethought of as reverse waypoints or virtual breadcrumbs defining thereturn path. Medical device 12 can then be robotically actuated tonavigate the return path by following the virtual breadcrumbs.

As one of skill in the art will understand, the higher the sampling ratefor measuring the position of medical device 12 as it navigatesnavigation path 200, the more reference points will be collected, andthe more reference points collected, the smoother the return path willbe. Accordingly, the resolution (e.g., the relative smoothness) of thereturn path may be user-adjustable; the user-selected resolution can beused to adjust the sampling rate to an appropriate value. Alternatively,the sampling rate may be directly user-adjustable.

As an alternative to navigating from final waypoint 202 b to firstwaypoint 202 a along a virtual breadcrumb return path, medical device 12may be navigated waypoint-to-waypoint in reverse along navigation path200. To implement this reverse navigation, a plurality of roboticsettings corresponding to the robotic settings used to robotically placemedical device 12 at each of the plurality of waypoints 202 definingnavigation path 200 are recorded in a memory device. These roboticsettings are then utilized to improve accuracy of travel of medicaldevice 12 along navigation path 200 in reverse, for example by playingthem back in reverse (i.e., retracting 0.5 mm and rotatingcounter-clockwise 30 degrees rather than advancing 0.5 mm and rotatingclockwise 30 degrees).

Navigation path 200 may be entirely in contact with tissue surface 82,or may include segments not in contact with tissue surface 82. Wherenavigation path 200 is entirely in contact with tissue surface 82,medical device 12 is navigated from first waypoint 202 a to finalwaypoint 202 b while maintaining contact between medical device 12 andtissue surface 82. Thus, controller 24 may advance medical device 12 toa location proximate starting point 202 a and periodically sense forcontact between medical device 12 and the moving cardiac surface. Uponsensing contact with the moving cardiac surface, movement of medicaldevice 12 may be synchronized with the movement of the cardiac surface.

Synchronization may be accomplished by measuring a contact force betweenmedical device 12 and tissue surface 82 and robotically actuatingmedical device 12 to maintain the contact force at a substantiallyconstant level or within a predetermined range of values. It should berecognized that the maximum contact force is associated with orthogonalpositioning of medical device 12 against tissue surface 82; asorthogonal contact is the preferred orientation for maximum efficacy oftreatment, it is desirable to also robotically actuate medical device 12to maintain the contact force at a substantially constant maximum level.It is also contemplated, however, that contact force feedback, forexample from a three-axis force sensor, may be utilized to roboticallyactuate medical device 12 to maintain other preset orientations relativeto tissue surface 82.

Alternatively, the contact sensing methodology disclosed herein could beutilized to monitor the proximity or degree of contact between medicaldevice 12 and tissue surface 82. For example, robotic surgical system 10may advance medical device 12 relative to the cardiac surface when therate of change in the contact force is indicative of the cardiac surfacemoving away from medical device 12 and retract medical device 12relative to the cardiac surface when the rate of change in the contactforce is indicative of the cardiac surface moving towards medical device12.

Medical device 12 may be used to administer a therapy or perform adiagnostic procedure as it is navigated along navigation path 200,either going forwards (i.e., while being introduced into the patient) orin reverse (i.e., while being retraced from the patient), or as medicaldevice 12 is navigated along the return path. Medical device 12 may bean ablation device, and the therapy may be ablating tissue alongnavigation path 200 with the ablation device. Alternatively, the therapymay involve utilizing medical device 12 to deliver a therapeutic agentto a tissue surface at one or more target points 204 along navigationpath 200. Therapy may be administered at one or more discrete locationsor substantially continuously along navigation path 200. Other therapiesand diagnostic procedures are also contemplated.

Automatic Creation of Ablation Lesions

Robotic surgical system 10 and the automatic therapy deliverymethodology disclosed herein, as well as one or more of the contactsensing, surface modeling, and diagnostic data mapping methodologies,may be advantageously utilized in combination to automatically createablation lesions on the cardiac surface. An ablation probe is installedinto robotic surgical system 10 as medical device 12. The ablation probecarries thereon one or more ablation elements, which may be RF elements,ultrasound elements, thermal elements, cryogenic elements, laserelements, microwave elements, or any other type of element fordelivering ablative energy or chemicals to tissue.

As described above, display 156 preferably presents a graphicalrepresentation of an area of tissue to be ablated, such as a portion ofthe patient's heart. User interface 166 may be used to select aplurality of target points 204 thereon as described herein. For example,the user may identify at least two target points 204 defining thepredetermined path on the graphical representation of surface 82 ofheart chamber 152. Alternatively, the user may trace a substantiallycontinuous treatment path 200 on the graphical representation.

User interface 166 is coupled to controller 24 such that controller 24may cause the ablation probe to ablate tissue along predetermined path200 at and between the plurality of target points 204. Path 200 may spana gap between first and second areas of ablated tissue as superimposedon the graphical representation of the cardiac surface.

Though the predetermined path is preferably user-designated through userinterface 166 as described above, it is also contemplated that path 200may be computer-determined. For example, the electrophysiology processormay analyze the cardiac surface in order to identify one or more gapsbetween ablated tissue, and define path 200 accordingly, in order tocreate a substantially continuous lesion.

Controller 24 robotically moves the ablation probe to an area near atissue surface. The controller 24 then advances the ablation probe intocontact with the cardiac surface and activates the ablation element (orelements) thereon. Once in contact with tissue surface 82 and active,the ablation probe is robotically moved along predetermined path 200while maintaining contact between the probe and the cardiac surface tocreate a substantially continuous ablation lesion. For example,controller 24 may advance the ablation probe to a point in the firstablated area, activate the ablation element or elements, and roboticallymove the ablation probe to a point in the second ablated area, therebyablating a path along the gap between the first ablated area and secondablated area. The result is a substantially continuous ablation lesionbetween the first and second ablated areas.

Alternatively, controller 24 may advance the ablation probe to a firsttarget point 204 or waypoint 202, from the first target point to asecond target point 204 or waypoint 202, from the second target point toa third target point 204 or waypoint 202, and so on until reaching afinal target point or waypoint. The result is a substantially continuousablation lesion following the plurality of target points 204 orwaypoints 202.

In order to maintain contact between the ablation probe and the cardiacsurface, the ablation probe may include a contact sensor, the output ofwhich is monitored for proximity or degree of contact between theablation probe and tissue surface 82. The contact sensor may be a forcesensor or a sensor 84 employed by the contact sensing methodologydisclosed herein. Feedback from the contact sensor may be used bycontroller 24 to orient the ablation probe at any desired angle totissue surface 82, including substantially orthogonal thereto, in orderto improve lesion quality.

In some embodiments of the invention, the movement of the ablation probeis synchronized to the movement of tissue surface 82 caused by patientmovement, patient respiration, and/or the beating of the heart.Synchronization may be accomplished by monitoring a parameter at tissuesurface 82 and actuating the ablation probe to maintain the parameterwithin a predetermined range of values. Synchronization may also beaccomplished by monitoring a rate of change in the parameter. When therate of change in the parameter indicates that tissue surface 82 ismoving away from the ablation probe, the ablation probe can beautomatically actuated to advance relative to tissue surface 82; whenthe rate of change in the parameter indicates that tissue surface 82 ismoving towards the ablation probe, the ablation probe can beautomatically actuated to retract relative to tissue surface 82.

Electrophysiology information may be collected via sensor 84 andmonitored during the ablation process in order to measure lesionquality. Typical electrophysiology information includes, withoutlimitation, changes in amplitude, changes in fractionation, changes inimpedance, peak power delivered, average power delivered, peaktemperature achieved, and average temperature achieved. Other parametersindicative of lesion quality, diameter, or depth may also be measuredwithout departing from the spirit and scope of the present invention. Inorder to ameliorate biasing effects in the electrophysiology informationcaused by RF ablation energy, an RF filter may be utilized. Based on thefeedback in the measured electrophysiology information, robotic surgicalsystem 10 may dynamically adjust one or more aspects of the treatment,including, without limitation, probe speed, probe orientation relativeto the tissue surface, probe position, the degree of contact between theprobe and the tissue surface, and the distance the probe moves along thetissue surface.

Further, according to the methods disclosed herein, the ablation lesionmay be created as the ablation probe is withdrawn from the patient. Anablation lesion created as the ablation probe is withdrawn may be ofbetter continuity, higher quality, and greater precision than anablation lesion created as the ablation probe is advanced. This benefitis particularly useful in more elongate lesions.

Although several embodiments of this invention have been described abovewith a certain degree of particularity, those skilled in the art couldmake numerous alterations to the disclosed embodiments without departingfrom the spirit or scope of this invention. For example, the roboticsurgical system 10 may be modified to incorporate additional servomechanisms and controllers operating on additional degrees of freedom.

Further, though the contact sensing methodology has been described inconnection with a robotically controlled medical device, it could alsobe implemented in a manually controlled medical device. It should alsobe understood that, rather than utilizing absolute values in the variouscontact sensing algorithms described herein, the thresholds or limitsmay be appropriately adjusted to compensate for negative values of ΔP,for example by taking the opposite of all thresholds or limits andreversing the comparator (i.e., changing < to >) upon detecting that ΔPis less than zero.

In addition, one of ordinary skill in the art will appreciate that,though the devices and methods disclosed herein have been described inconnection with the treatment of atrial fibrillation, and in particularin connection with the creation of lesions of ablated tissue, they maybe used to administer other therapies or to perform other diagnosticprocedures. For example, the automatic therapy delivery method disclosedherein could be utilized to emplace a pacemaker lead or a stent or toperform a balloon angioplasty. It is also contemplated that the ablationlesions may be automatically created without utilizing one or more ofthe methods disclosed herein. For example, rather than creating thesurface model of the patient's heart chamber utilizing the surfacemodeling methodology disclosed herein, navigation path 200 may bedefined on an MRI- or CT-generated surface model.

Further, the devices and methods disclosed herein are capable of useboth epicardially and endocardially.

All directional references (e.g., upper, lower, upward, downward, left,right, leftward, rightward, top, bottom, above, below, vertical,horizontal, clockwise, and counterclockwise) are only used foridentification purposes to aid the reader's understanding of the presentinvention, and do not create limitations, particularly as to theposition, orientation, or use of the invention. Joinder references(e.g., attached, coupled, connected, and the like) are to be construedbroadly and may include intermediate members between a connection ofelements and relative movement between elements. As such, joinderreferences do not necessarily infer that two elements are directlyconnected and in fixed relation to each other.

It is intended that all matter contained in the above description orshown in the accompanying drawings shall be interpreted as illustrativeonly and not limiting. Changes in detail or structure may be madewithout departing from the spirit of the invention as defined in theappended claims.

What is claimed is:
 1. A method of navigating a medical device through a body of a patient, the method comprising: providing a topography of at least a portion of the body; accepting user input defining a navigation path comprising a plurality of waypoints on the topography, the plurality of waypoints including a first waypoint and a final waypoint; robotically navigating the medical device to the first waypoint; and robotically navigating the medical device along the navigation path from the first waypoint to the final waypoint.
 2. The method according to claim 1, further comprising administering a therapy with the medical device while robotically navigating the medical device along the navigation path.
 3. The method according to claim 2, further comprising: robotically navigating the medical device along a return path from the final waypoint to the first waypoint; and administering a therapy with the medical device while robotically navigating the medical device along the return path.
 4. The method according to claim 3, wherein the return path comprises a plurality of reference points, and wherein the plurality of reference points is generated by periodically measuring a position of the medical device while navigating the medical device along the navigation path from the first waypoint to the final waypoint.
 5. The method according to claim 4, wherein a sampling rate for periodically measuring a position of the medical device is adjustable.
 6. The method according to claim 5, wherein the sampling rate is user-adjustable.
 7. The method according to claim 4, wherein a resolution of the return path is user-adjustable.
 8. The method according to claim 3, wherein administering a therapy with the medical device while robotically navigating the medical device along the return path comprises ablating tissue with the medical device.
 9. The method according to claim 3, wherein administering a therapy with the medical device while robotically navigating the medical device along the return path comprises utilizing the medical device to deliver a therapeutic agent to a tissue surface at one or more target points along the return path.
 10. The method according to claim 2, wherein the medical device comprises an ablation device, and wherein administering a therapy with the medical device comprises ablating tissue with the ablation device.
 11. The method according to claim 2, wherein administering a therapy with the medical device comprises utilizing the medical device to deliver a therapeutic agent to a tissue surface at one or more target points along the navigation path.
 12. The method according to claim 1, wherein the step of providing a topography of at least a portion of the body comprises providing a graphical representation of the topography through a user interface, and wherein the step of accepting user input defining a navigation path comprising a plurality of waypoints on the topography comprises accepting user input defining the plurality of waypoints on the graphical representation through the user interface.
 13. The method according to claim 12, wherein accepting user input defining the plurality of waypoints on the graphical representation through the user interface comprises accepting user input through a pointing device.
 14. The method according to claim 12, wherein accepting user input defining the plurality of waypoints on the graphical representation through the user interface comprises accepting user input through a touchscreen.
 15. The method according to claim 1, further comprising robotically navigating the medical device in reverse along the navigation path.
 16. The method according to claim 15, further comprising using the medical device to administer a therapy while the medical device is being robotically navigated in reverse along the navigation path.
 17. The method according to claim 15, further comprising: recording in a memory device a plurality of robotic settings, the plurality of robotic settings corresponding to robotic settings that were used to robotically place the medical device at each of the plurality of waypoints that define the navigation path; wherein the step of robotically navigating the medical device in reverse along the navigation path utilizes the plurality of recorded robotic settings to improve accuracy of travel of the medical device along the navigation path in reverse.
 18. The method according to claim 1, wherein the step of robotically navigating the medical device along the navigation path from the first waypoint to the final waypoint comprises robotically navigating the medical device along the navigation path from the first waypoint to the final waypoint while maintaining contact between the medical device and a tissue surface.
 19. The method according to claim 18, wherein the step of robotically navigating the medical device along the navigation path from the first waypoint to the final waypoint while maintaining contact between the medical device and a tissue surface comprises: measuring a contact force between the medical device and the tissue surface; and robotically actuating the medical device to maintain the contact force between the medical device and the tissue surface at a substantially constant level. 